Technical Field
The present invention relates to a liquid crystal display device and, more particularly, to improvement in electrostatic discharge resistance of a liquid crystal display device.
Related Art
In a FFS (Fringe Field Switching) mode liquid crystal panel, a pixel electrode and a common electrode, which control the alignment of liquid crystal, both are provided in an element substrate, and these two electrodes are laminated through an insulating film. Of these electrodes, an upper layer electrode is provided with slits. A rubbing process is treated in a direction that is substantially parallel to a long side direction of the slits. When the electric potential between the electrodes is an off potential, liquid crystal molecules are aligned in a direction that is perpendicular to the long side direction of the slits. When an electric potential higher than the off potential is applied between the electrodes, an electric field (horizontal electric field) is generated in a direction perpendicular to the long sides of the slits, and liquid crystal molecules are rotated (horizontally rotated) in a plane parallel to the substrate along the direction of the electric field. By controlling the rotation angle of the liquid crystal molecules, the amount of light transmission is controlled.
Note that, in addition to the FFS mode, an IPS (In-Plane Switching) mode is known as a configuration in which both the pixel electrode and the common electrode are provided in the element substrate.
Liquid crystal panels have been progressively reduced in size, thickness, and window frame width, and progressively added with functions, such as a touch panel. In accordance with the above, static electricity from the outside of the panels through a human body, or the like, may cause a trouble in the panels.
For example, in the FFS mode, and the like, when an opposite substrate, which is opposed to an element substrate, is applied with static electricity and is electrostatically charged, there is a possibility that a vertical electric field is generated by the electrostatic charge and, hence, an appropriate alignment control on the liquid crystal using the electrodes provided in the element substrate cannot be performed. In this case, for example, in a normally black liquid crystal panel, a black display becomes whitish and the contrast is decreased. In addition, when a degree of whitish display is not uniform over the entire screen, display chrominance non-uniformity is observed.
As one of countermeasures to the above, there is a manner in which a translucent conductive film is formed over the entire outer surface of the opposite substrate, and this translucent conductive film is connected to a case or an FPC (Flexible Printed Circuit) terminal, thus releasing the electrostatic charge to the ground electric potential (GND) of an external circuit, which is described in Japanese Unexamined Patent Application Publication No. 9-105918.
Even with the above countermeasure, however, it has been found that there is a possibility that a sufficient electrostatic discharge resistance cannot be obtained.